The present invention relates to a radio apparatus used in a digital mobile communication system and the like, and more particularly, to a radio apparatus and transmission/reception method used in a CDMA (Code Division Multiple Access) mobile communication system.
FIG. 1 is a block diagram illustrating a configuration of a conventional radio apparatus. The conventional radio apparatus illustrated in FIG. 1 is used in a radio system such that a reception frequency is only switched to another frequency at the time a transmission signal is transmitted so as to obtain a level measurement on a reception frequency channel that is different from an ordinary transmission/reception frequency combination and further obtain system control information.
Radio apparatus 10 is provided with D/A converters 11 and 12 to which I channel data and Q channel data (hereinafter, respectively referred to as I data and Q data) is respectively input, low-pass filters 13 and 14, quadrature modulator 15, gain control amplifier 16, band-pass filter 17, up-mixer 18, band-pass filter 19, and power amplifier 20. Radio apparatus 10 is further provided with antenna duplexer 21 and antenna 22. Radio apparatus 10 is furthermore provided with low noise amplifier 23, band-pass filter 24, down-mixer 25, band-pass filter 26, gain control amplifier 27, quadrature demodulator 28, low-pass filters 29 and 30, and A/D converters 31 and 32 that respectively output I data and Q data. Still furthermore, radio apparatus 10 is provided with transmission IF (intermediate) frequency synthesizer 33, transmission RF (radio) frequency synthesizer 34, reception RF frequency synthesizer 35, and reception IF synthesizer 36.
The next explanation is given of the transmission processing operation in radio apparatus 10.
I data and Q data to be transmitted is converted into respective analog signals in D/A converters 11 and 12, subjected to low-pass filtering in low-pass filters 13 and 14, and then converted in quadrature modulator 15 into a signal with a transmission IF frequency using a signal generated from transmission IF frequency synthesizer 33, respectively.
The converted signal with the transmission IF frequency is amplified in gain control amplifier 16 corresponding to a control voltage, filtered in band-pass filter 17 to pass a signal with a predetermined frequency band, and then converted in up-mixer 18 into a signal with a transmission RF frequency using a signal generated from transmission RF frequency synthesizer 34.
The converted signal with the transmission RF frequency is filtered in band-pass filter 19 to pass a signal with a predetermined frequency band, amplified in power amplifier 20, and output to antenna duplexer 21 that separates a transmission frequency signal and reception frequency signal, whereby the radio signal is transmitted from antenna 22.
The next explanation is given of the reception processing operation in radio apparatus 10.
A quadrature modulated signal with a reception frequency received at antenna 22 is output to antenna duplexer 21 which separates a transmission frequency signal and reception frequency signal. The resultant signal is subjected to low noise amplification in low noise amplifier 23, filtered in band-pass filter 24 to pass a signal with a predetermined frequency band, and then converted in down-mixer 25 into a signal with a reception IF frequency using a signal generated from reception RF frequency synthesizer 35.
The converted signal with the reception IF frequency is filtered in band-pass filter 26 to pass a signal with a predetermined frequency band, amplified in gain control amplifier 27 corresponding to a control voltage, subjected to quadrature demodulation in quadrature demodulator 28 using a signal generated in reception IF frequency synthesizer 36, and then demodulated to an I signal and Q signal.
The I signal and Q signal are subjected to low-pass filtering in low-pass filters 29 and 30, and converted into respective digital signals in A/D converters 31 and 32, respectively, whereby I data and Q data are output.
It is herein assumed that a transmission RF frequency is ft, a reception RF frequency is fr, and that the ft and fr have a relationship of fr greater than ft, the transmission RF frequency and reception RF frequency are specified so that fr minus ft (frxe2x88x92ft) is constant.
Accordingly, assuming that a frequency of transmission IF frequency synthesizer 33 is f1, a frequency of transmission RF synthesizer 34 is f2, a frequency of reception RF synthesizer 35 is f3, and that a frequency of reception IF frequency synthesizer 36 is f4, the transmission RF frequency ft is expressed with f2xe2x88x92f1 or f2+f1, the reception RF frequency fr is expressed with f3xe2x88x92f4 or f3+f4, and f2 equals f3 (f2=f3) at the time of the ordinary operation where frxe2x88x92ft is constant.
When a signal is received which has a reception RF frequency frxe2x80x2 where fr-ft is not constant, i.e., when f2 greater than f3 or f2 less than f3, the frequency of reception RF synthesizer 35 is switched corresponding to the reception frequency frxe2x80x2 that is different from fr. In this case, a quadrature modulated signal with the reception frequency frxe2x80x2 received at antenna 22 is output to antenna duplexer 21 while being separated from a signal with the transmission frequency, subjected to low noise amplification in low noise amplifier 23, filtered in band-pass filter 24 to pass a signal with a predetermined frequency band, and subjected to frequency conversion in down-mixer 25 using a signal with a frequency generated in reception RF frequency synthesizer 35 corresponding to the reception frequency frxe2x80x2 so that the reception frequency is the same as a case that the reception IF frequency is fr.
In the above-mentioned conventional apparatus, however, when a signal is received which has a frequency different from usually specified one in a communication, it is necessary to fast switch a frequency of reception RF frequency synthesizer 35, and further to concurrently operate reception RF frequency synthesizer 35 and transmission RF frequency synthesizer 34, thereby resulting in a problem that current consumption becomes great.
It is an object of the present invention to provide a radio apparatus and transmission/reception method capable of performing frequency switching fast and with low current consumption in the case of receiving a signal with a frequency different from ordinary specified one.
This object is achieved by generating in a common frequency synthesizer a first frequency signal with a transmission frequency and reception frequency combined, generating in a reception frequency synthesizer a second frequency signal with a frequency different from that of the first frequency signal, combining in a transmission mixer the first frequency signal and quadrature modulated transmission I and Q signals, and at the time of ordinary communications, combining in a reception mixer the first frequency signal and a received signal, while only at the time of receiving a signal with a frequency different from the first frequency, operating the reception frequency synthesizer to combine the received signal with the second frequency signal.